Template for PRACTICES.md

[gonsie]

The first part of the PSIP process is documenting a team’s current practices. Teams would fill in the values and document could live in PRACTICES.md within the repo (possibly in the .github folder to prevent clutter). Teams would add/remove items as they saw fit.

Categories and starter item suggestions are welcome!

Due to my fat fingers, I accidentially committed this document directly on the master branch. I had intended for it to be cooperatively developed in a PR before merging... oops.